The present invention relates to dynamoelectric machines, and more particularly, to such machines having armature conductors located in the air-gap. The instant invention is particularly drawn to a fastening technique to secure the armature conductors to the stator frame, under constant mechanical compression.
In certain dynamoelectric machines, the armature conductors are located within the air-gap separating the stator and the rotor, rather than in slots located between iron teeth. The electromechanical loads to which conductors are subjected within the air-gap are substantially greater than the loads applied to armature conductors located in the stator iron, since the magnetic field strength at the conductor is substantially greater in the former case. Furthermore, the electromechanical load direction rotates synchronously in the radial plane. If these forces were permitted to create relative motion between adjacent surfaces, fretting and abrading of the insulation layer on the conductors would result. Under abnormal operations, for example suddenly applied short circuits or synchronization out of phase, the electromagnetic forces on the conductors can be many times the normal operation forces for short periods of time. These forces can be of such a magnitude that damage to the relatively weak ground wall insulation on the conductors may result, unless the conductors are maintained in a state of compression. Electromagnetic design considerations dictate that the fraction of the air-gap volume devoted to conductor and insulation be as large as possible consistent with mechanical requirements of the conductor support structure. Consequently, an optimum support structure for armature conductors must provide secure mounting of the conductors without requiring massive structure.
In order to limit electrical losses within the armature conductor mounting structure, nonconductive structural materials are usually required for mounting the armature conductors. Fiber-reinforced plastics have been conventionally used because of their combination of strength and toughness in addition to being nonconductive. See, for example, U.S. Pat. No. 4,214,182 issued July 22, 1980 to Keim, and assigned to the instant assignee and incorporated herein by reference. However, plastics are not as readily fabricated to close tolerances as are metals. Also, plastics are subject to shrinkage, creep and relaxation to some extent.
Therefore, an armature conductor mounting structure must be able to compensate for small variations in size of the support members and for size changes over time without loss of firm support of the conductors.
Accordingly, an object of the invention is to provide a means to attach armature conductors to the stator of a dynamoelectric machine within the air-gap in such a way that the bars and their support means are held in compression in both the circumferential and radial directions.
A further object is to provide a mounting arrangement such that the compressive load applied to the armature conductors is maintained essentially constant regardless of minor changes or variations in the conductor support structure.